Microphone



J.L.SNOEK Oct. 9, 1934.

MICROPHONE Filed Dec. 17. 1952 2 Sheets-Sheet l INVENTOR- JACOB MSSMEKa. 9, 1934. J L SNOEK 1,976,692

MICROPHONE Filed Dec. 17. 1932 2 Sheets-Sheet 2 102 w m w m m 110 v I30a: 1. I00 I00 s0 1/ 5 90 u 90 v I M I 00 x s0 5a P00203040 Maze/3040001010 Y 250,500, 000

INVENTOR- ATTORNEY- Patented Oct. 9, 1934 UNITED STATES PATENT OFFICEMICROPHONE poration of Delaware Application December 17, 1932, SerialNo. 647,728 In the Netherlands December 5, 1931 5 Claims. (Cl. 179-423)to simplify and general rule these limited angular directions are withina conehaving an opening angle of about 90 the axis of which is at rightangles with the active microphone surface.

All other vibrations reaching the microphone in another direction thanthose whose axesare right angles to the active surface of themicrophones are sensitive only in so far as low frequency vibrations areconcerned. In such a case the microphones react very unsatisfactorily toI high frequency vibrations, for instance/those of more than 2000cycles.

Consequently, microphones having a pronounced directional effect lendthemselves as a general rule for satisfactorily picking up ofunidirectional sound waves, because there it is possible to choose afavourable position for the microphone.

However, it will be appreciated, that whenever using microphones havinga pronounced directional effect in the case of sound waves that are tobe picked up which are produced by a plurality of different soundsources, for instance by an orchestra, it is not possible to choose aposition which is suitable for each one of the instruments. 1

Insuch a case a {microphone will be required having no, or substantiallyno. directional effect.

The present invention has for its principal purpose to provide means ,bywhich it is rendered possible to provide a microphone which may beadjusted in such a manner that it hasa more or less pronounced or evenno directional eflect at all, according to whether the circumstancesunder which the microphone is used require it to be so.

The microphone according to this invention thereupon be. connectedtogether. The pick-up elements may be constructed in accordance with theelectrodynamic, electrostatic or electromagnetic principle. Furthermorepick-up elements may be used comprised of separate chambers whichcontain the electrodes and are filled with carbon granules, the separatechambers being shutoff by a diaphragm. These latter well known form ofmicrophones have a pronounced directional eflect.

The central support body preferably consists of a solid block of amaterial having the property of damping the vibrations and of beingsuitable electrically insulating, for instance such material as marbleor alabaster may be used. Consequently, according to the invention thepick-up elements of the microphone may be secured to the periphery ofthe central support block, for instance, in form of a cube.

' However, it is also possible to interconnect the 7 It appears thatwith a suitable coupling arrangement of the pick-up elements thedirectional effect of such a microphone is considerably less pronouncedthan that of each of the pick-up elements separately. However, thepickup elements may also be connected in such a manner that a verystrong directional effect is obtained. As stated above, this may bedesirable in some cases.

' With reference to obtaining the proper working of the pick-up elementsof the microphone they may be properly controlled by placing themicrophone in or on a suitable rotary device at a certain distance apartfrom a stationary sound source, the tone of the stationary sound may beadjusted to a definite frequency. To the microphone terminals there isapplied a proper working potential. An indicating instrument is thenconnected in the microphone line and the deflection of the instrument ismeasured for difierent positions of the microphone pick-up elements withrespect to the constant direction from which the sound arrives. In thismanner a polar diagram is obtained, of which some examples will beexplained hereinafter with reference to Figs. 4a, 4b and 4c of thedrawings.

I have found that it appears from making such a diagram that amicrophone according to the invention, in which three or four pick-upelements are provided at the periphery of a central support body with anarrangement of the pick-up elements in such a manner that all pick-upelements behave uniformly with respect to the electric currents, has aconsiderable supporting bodies.

parallelopipedon at the side faces of which the pick-up elements arearranged. However, it is also possible but less simple from a point ofview of manufacture, to provide the pick-up elements located around theperiphery of a cylindrical body.

In a preferred form of construction of this invention the adjacentelectrodes of the pick-up elements are secured to a common supporting-member and placed in a cavity of the central support body.Consequently, if four pick-up elements are provided there are alsoprovided four In this case the central support body is provided withfour perforations for receiving the supporting bodies. By means ofsuitable screws the electrodes may be secured to the supporting bodies.It is more practical to make the supporting bodies entirely or partly ofan electrically conducting material. In this case the supporting bodiesmay be given such a' size that they will project slightly outward fromthe central support body, so that they may also serve for connectingsuitable conductors to the microphone.

For clamping the diaphragm of the pick-up elements to the central bodyuse is made of frames or frame-like members which are secured to thecentral body by means of screws or bolts. In one form of constructionaccording to this invention the frames and the electrodes are fixed bythe same means to the supporting bodies. In this manner a simpleconstruction of the microphone is obtained.

With microphones according to this invention sound is picked up asfollows. When it is consideredwhat properties are required by the retary method mentioned above with respect to the directional effect theelements are then con: nected in series, in parallel or inseries-parallel so that the desired effect is then obtained.

Several further important advantages of this microphone will be setforth by referenceto the several forms of construction represented in'the drawings.

Fig. 1 is a perspective view of a carbon form V of microphoneconstruction according to this invention.

Fig. 2 is a partial cross section of. microphone construction along theline 22 of Fig.1. n Fig. 2a is a section along the line 2a of Fig. 2.

Figs. 3a, 3b and 30 represent several different circuit couplingarrangements of pick-up elements according to this form of microphoneconstruction.

Fig. 4 shows several polar diagrams of the type referred to which areobtained in this manner and which more clearly illustrate thedirectional effect of the microphone according to the invention. v

Referring now in detail to Fig. 1, 1 denotes a prismatical blockconsisting of an antivibratory material, such as of marble or alabaster.This PM. These are absolute but relative values.

support body 1 is provided with four perforations extending in parallelwith the upstanding ribs and in which four supporting bodies 2 areprovided. The four carbon granual chambers 3 are clearly shown in Fig.2. Each chamber is limited at the side walls by electrodes 4, while atthe front side a slight projection is obtained by means of a diaphragm 5consisting, for instance, of a mica sheet. The diaphragm and theelectrodes are clamped as indicated in Fig. 2a between the central body1 and the securing frames 6 of insulating material by means of screws 7screwed into the supporting bodies 2.

As indicated,in Fig. 1 the supporting bodies project from the bottom ofthe central body 1, so that they may serve as a connecting point forconductors. In this case the supporting bodies must consist at leastpartly of electrically conducting material.

Fig. 3a indicates diagrammatically the manner in which the electricconductors are connected I only at A and B. A, B, C and D denote thejunction terminals of the supporting bodies 2. It will be obvious thatwith this arrangement the branch ADCB is traversed by a weak currentonly so that the microphone works substantially as the normal orordinary form of microphone with one pick-up element only. Thecorresponding polar diagram (Fig. 4a) shows that the microphone has avery strong directional effect with this arrangement.

In the polar diagrams according to Figs. 4a, 4b and 40 it must beimagined that the sound waves always 'come from the direction PM whereasthe microphone, which is placed at M is turned over angles of 0 to 180with respect to this line. variations produced for tones of differentfrequency are plotted radially as a function of the angle of themicrophone with respect to the line In fact, for the sake of conveniencethe adjustment of the measuring device for difierent frequencies is suchthat with each manner of connection the sensitivenessof the microphonein the direction PM is the same for all frequencies. Consequently forjudging the microphone in the different arrangements only the form ofthe various curves must be considered. r

The solid lines in the diagrams hold good for frequencies of 4000 and3000 cycles respectively, the dotted lines for those of 2000 cycles, andthe dash and dot lines for vibrations having a frequency of 250, .500and 1000 cycles respectlvely.

It will be appreciated that in the arrangement shown in Fig. 3a the lowfrequencies are sufficiently taken up in every position of themicrophone. The high frequencies on the contrary are taken up only whenthe element lying in the plane AB extends entirely or substantiallyentirely at right angles to the direction PM and if it is turned to thesound direction.

Consequently with this arrangement the microphone is poorly adapted fortaking up music The values of the currentcoming from various directions,for instance,

orchestra music. This holds also good for the arrangement shown in Fig.3b. 'In this arrangement the microphone behaves as if it consisted inthis arrangement is still better adapted than in the arrangement shownin Fig. 3a.

A very uniform sensitiveness to different frequencies is obtained,however, when constructing the arrangement as shown in Fig. 3c. This isgraphically indicated in Fig. 4b. Consequently in this arrangement themicrophone according to the invention is particularly adapted for takingup sound waves not coming from various directions.

However, the microphone according to this invention has the advantagethat the arrangement may also be such that there is a distinctdirectional effect, since by a simple changing over the microphone maybe brought into the most favourable condition on one hand for taking upsound waves coming from a single direction and on the other hand fortaking up sound waves coming from various directions.

A carbon microphone pick-up element according to the invention containsa particularly large member of active carbon particles, as it is wellknown that especially carbon microphones have the disagreeable propertyof producing an annoying buzzing noise.

The cause of this noise which is usually noticed by buzzing of themicrophone is believed to be tight packing of.the carbon particles. Ihave found that the buzzing usually strongly decreases when increasingthe number of active carbon particles. Therefore, it isadvisable to givethe carbon chamber a constant cross section.

It has been found that the buzzing is inversely proportional to therootof the number of active carbon particles so that a microphoneaccording to this invention comprising four elements must produce abuzzing which is twice as small as that of a microphone comprising oneelement only. In fact, experiments have proved that this isapproximately the case.

Furthermore, it has been found that the surface or active area of thediaphragm must be large so as to reduce the buzzing.

It will be obvious to those skilled in the art that a carbon microphoneaccording to this invention satisfies all'of these conditions.Consequently the buzzing of such a microphone is materially smaller thanthat inherent to known forms of construction.

I claim:

1. A microphone comprising a plurality of cated substantially in -eachcorner of said body,

a plurality of metallic supporting members passing through the aperturesin said body, and means on said supporting members for electricalconnection of said pick-up elements.

2. A microphone comprising a plurality of pick-up elements having carbongranules located on the side faces of a cubical support body havingapertures located substantially in each corner of said body, a pluralityof metallic supporting members passing through the apertures in saidbody, and means on said supporting members for electrical connection ofsaid pick-up elements.

3. A microphone comprising a plurality of pick-up elements located onthe side faces of a cubical support body having apertures locatedsubstantially in each corner, a plurality of metallic supporting memberspassing through the apertures in said body, a threaded stud and abinding post on the lower portion of said supporting members forelectrical connection of said pick-up elements.

4. A microphone comprising a plurality of pick-up elements, said pick-upelements located on the side faces of a cubical support body havingapertures located substantially in eachcorner of said body, said pick-upelements comprising carbon granules retained on four faces of saidsupport body by a frame-like member and a diaphragm, both the saidframe-like member and the'said diaphragm being secured to said supportbody by retaining means joined to a plurality of metallic support.members passing for altering the electrical connection on said pick-upelements to modify the directional effect of said pick-up elements.

JACOB LOUIS SNOEK.

